1. Field of the Invention
The present invention relates to a transmission-reception diplexer having a transmission channel for forwarding radio-frequency transmission signals onto an antenna which is connectible to an antenna terminal and having a receiving channel for forwarding a signal received from the antenna to a receiver, whereby at least one diode is provided in the receiving channel as a radio-frequency (RF) switch.
2. Description of the Prior Art
Transmission-receiving diplexers are used in order to alternatively connect a transmitter and a receiver to an antenna. A transmitting-receiving diplexer therefore represents nothing more than an antenna switch and electrically corresponds to a mechanical switch-over device.
A transmitting-receiving diplexer of the type initially set forth is described in the book by Erich Renz, "PIN und Schottky-Dioden", Heidelberg 1976, pp. 121-122. The diode in the receiving channel is biased either in the conducting direction or the non-conducting direction by a DC voltage. High requirements are therefore made of the diode in the receiving channel. First of all, the diode must keep the relatively-powerful transmission signal away from the receiver. Secondly, a relatively weak received signal in the receiving mode must be forwarded from the antenna to the receiver with optimally little attenuation. For inhibiting the receiving channel, the inhibiting DC voltage must be at least as high as the amplitude of the transmission voltage. Producing the inhibit voltage is not discussed in greater detail in the aforementioned reference.
U.S. Pat. No. 4,673,831, fully incorporated herein by this reference, proposes a number of circuits for radio-frequency switches having diodes that require an extremely-low energy for inhibiting or conducting. With these circuits, however, it is not possible to block higher powers because the PIN diodes employed have high off-state power losses. In one version, an inhibit voltage from an external voltage source is applied to the diodes therein in order to achieve a faster switching and a better separation.